Tissue ablation is used in numerous medical procedures to treat a patient. Ablation can be performed to remove undesired tissue such as cancer cells. Ablation procedures may also involve the modification of tissue without removal, such as to interfere with or stop electrical propagation through cardiac tissue in a patient with an arrhythmia. Often the ablation is performed by passing energy, such as electrical energy, through one or more electrodes to cause the tissue in contact with the electrodes to heat up to an ablative temperature. Other electrical energies such as laser, microwave, ultrasound, etc., can effect change in tissue. Alternatively, non-electrical therapies such as medications, stem cells, biologics, or cryotherapy can be used to alter the structure and function of tissue.
Atrial fibrillation refers to a type of cardiac arrhythmia where there is disorganized electrical conduction in the atria causing rapid uncoordinated contractions that result in ineffective pumping of blood into the ventricle and a lack of synchrony. During atrial fibrillation, the atrioventricular node receives electrical impulses from numerous locations throughout the atria (such as the pulmonary veins) instead of only from the sinus node. This condition overwhelms the atrioventricular node, resulting in an irregular and rapid heartbeat. As a result, blood pools in the atria and increases the risk of blood clot formation.
Atrial fibrillation treatment options are limited. Three known treatments, lifestyle change, medical therapy and electrical cardioversion, all have significant limitations. Electrical cardioversion attempts to restore sinus rhythm but has a high recurrence rate. In addition, if there is a blood clot in the atria, cardioversion may cause the clot to leave the heart and travel to the brain or to some other part of the body, which may lead to a stroke.
Various ablation techniques have been proposed to treat atrial fibrillation, including the Cox-Maze procedure, linear ablation of various regions in the atrium, and circumferential ablation of pulmonary vein ostia. Other linear lesions can target the roof of the left atrium, the mitral valve isthmus, superior vena cava, and the ligament of Marshall.
Certain types of arrhythmias have critical components that require ablation near the normal conduction system of the heart (AV junction and/or His bundle). These arrhythmias typically include paraseptal bypass tracts, AV node reentrant tachycardia, and certain atrial and ventricular tachycardias. Inadvertent ablation misapplications in treating such problems may result in complete heart block and require implantation of a permanent pacemaker, a known possible complication of the procedure. In addition, other untoward events may occur during ablative procedures in which the body may exhibit early signs (such as a change in heart rate, oxygen saturation, and/or blood pressure) which may indicate perforation. When this occurs, the device or catheter creates a hole in the heart wall leading to fluid accumulation in the pericardial sac and a life-threatening condition called cardiac tamponade. Blood needs to be rapidly removed from the pericardial sac by a needle or surgical window along with any supportive measures (blood and/or fluids) as well as possible surgical repair. Each and every untoward event has the potential for medical legal action in which any delay in terminating therapy may be highly scrutinized.
In applying ablation techniques to treat arryhthmias, the distal tip of an ablation catheter is advanced to a desired location in a patient's heart. Radiofrequency or laser energy, for example, is transmitted to the distal tip of a catheter from a point adjacent and/or external to a catherization laboratory upon signal from the doctor or operator to a technician or nurse who operates a generator (such as an RF generator) or a laser, to deliver ablation therapy or energy. Whenever the doctor or operator wants the ablation therapy or energy to be discontinued, the doctor or operator signals the technician or nurse, usually by voice command (“Stop!!!” or “Off!”). However, there is an inherent delay in this procedure, which could result in damage to a patient, such as heart block, perforation, or phrenic nerve paralysis, if the ablation energy is not terminated quickly enough. In addition, it is not very practical for the sterile catheter operator to have direct and immediate control over any switching mechanism contained on the non-sterile generator or console to terminate therapy as they are concurrently configured. Also, these ablation generators and consoles are typically not easily accessible to the operator and, if placed in such a location, would potentially be disruptive to lab staff and operations. Alternatively there could be foot control for the doctor or operator to terminate the ablation energy, but using a foot control may be awkward and difficult to control (especially because two foot pedals would potentially be used in concert: one for fluoroscopy and the other for an on/off switch). In addition, accidentally stepping on the on/off foot pedal switch as it currently functions can potentially turn on therapy and cause inadvertent ablative therapy delivery with unintended injury to the heart, its conduction, and other structures.
Medical devices having on/off or cut-off mechanisms are known. See, for example, U.S. Pat. Nos. 5,951,461, 6,165,206, 6,235,022, 6,808,499, 7,717,932, and 7,763,033 and U.S. Published Patent Applications Nos. 2007/0233044, 2008/0245371, and 2009/0182325. However, none of these medical devices is an ablation catheter system useful for a cardiac ablation procedure, nor do any of the devices meet the unique demands characteristic of use of an ablation catheter in a catherization laboratory setting. In addition, a method and switching mechanisms have been developed which are compatible with a number of different ablation/therapy systems to prevent inadvertent therapy delivery and provide immediate manual control to the operator.